Radio positioning system

Abstract

A radio positioning system includes a plurality of base stations, each receiving a radio wave from a mobile terminal, and including a first base station whose position coordinates are known and a second base station whose position coordinates are unknown. The system also includes a distance measuring unit that measures a distance between the first and the second base stations based on the exchanging the radio waves; a position-coordinate calculating unit that calculates position coordinates of the second base station based on the measured distances; a determination control unit that determines a time reference station out of the base stations, and controls the time reference station to transmit a time reference pulse; and a distance-measurement control unit that calculates, using the time difference, a time difference between reception times of the wave signal at the base stations, and calculates position coordinates of the mobile terminal based on the time difference.

1 . A radio positioning system, comprising:
 a plurality of base stations, each receiving a radio wave from a mobile terminal, and including a first base station whose position coordinates are known and a second base station whose position coordinates are unknown;   a distance measuring unit that measures a distance between the first and the second base stations based on a result of exchanging radio waves between the first and the second base stations;   a position-coordinate calculating unit that calculates position coordinates of the second base station based on the measured distance;   a determination control unit that determines a time reference station out of the base stations, and controls the time reference station to transmit a time reference pulse; and   a control unit that calculates a time difference between reception times at which the base stations receive the wave signal from the mobile terminal, and calculates position coordinates of the mobile terminal based on the time difference.   
   
   
       2 . The radio positioning system according to  claim 1 , wherein the determination control unit calculates maximum values of distances between the respective base stations and the other base stations based on the result of the measurement to determine a base station having a smallest maximum value among the calculated maximum values as the time reference station. 
   
   
       3 . The radio positioning system according to  claim 1 , further comprising a counting unit that selects a base station out of the plurality of base stations and counts a number of other base stations, distances to which from the selected base station can be measured, wherein
 the determination control unit determines the time reference station based on a result of the counting of the counting unit, a base station having a largest number of other base stations, distances to which from the selected base station can be measured.   
   
   
       4 . The radio positioning system according to  claim 1 , wherein the determination control unit measures distances from the other base stations a plurality of times in the distance measuring unit for each of the base stations, calculates fluctuations in the measured distances, calculates maximum values of the fluctuations, and determines a base station having a smallest maximum value among the calculated maximum values as the time reference station. 
   
   
       5 . The radio positioning system according to  claim 1 , further comprising a reception-state monitoring unit that monitors a reception state in a base station that receives the time reference pulse, wherein
 the determination control unit switches the time reference station, when determining based on a result of the monitoring of the reception-state monitoring unit that the base station does not receive the time reference pulse for a predetermined time or more.   
   
   
       6 . The radio positioning system according to  claim 5 , wherein the determination control unit determines, based on the result of the measurement and the result of the monitoring, priority order of the base station that transmits time reference pulse, and switches, based on the determined priority order, the base station that transmits the time reference pulse. 
   
   
       7 . The radio positioning system according to  claim 6 , wherein the determination control unit controls the base stations to transmit the time reference pulse from different base stations at first timing and second timing and determines the time reference station, based on reception states in the respective base stations of the time reference pulse transmitted at the first timing and reception states in the respective base stations of the time reference pulse transmitted at the second timing. 
   
   
       8 . The radio positioning system according to  claim 1 , wherein the distance measuring unit measures distances among the respective base stations at every predetermined time. 
   
   
       9 . The radio positioning system according to  claim 8 , wherein the distance measuring unit measures distances among the respective base stations at timing different from timing when the time reference pulse is transmitted. 
   
   
       10 . The radio positioning system according to  claim 1 , wherein an ultra wide band (UWB) pulse is used for radio communication among the base stations and radio communication between the respective base stations and the mobile terminal. 
   
   
       11 . A radio positioning server apparatus used in a system including a plurality of base stations each receiving a radio wave from a mobile terminal, the base stations including a first base station whose position coordinates are known and a second base station whose position coordinates are unknown, the apparatus comprising:
 a distance measuring unit that measures a distance between the first and the second base stations based on a result of exchanging radio waves between the first and the second base stations;   a position-coordinate calculating unit that calculates position coordinates of the second base station based on the measured distance;   a determination control unit that determines a time reference station out of the base stations, and controls the time reference station to transmit a time reference pulse; and   a control unit that calculates a time difference between reception times at which the base stations receive the wave signal from the mobile terminal, and calculates position coordinates of the mobile terminal based on the time difference.   
   
   
       12 . A method of radio positioning a mobile terminal in a system including a plurality of base stations, the base stations including a first base station whose position coordinates are known and a second base station whose position coordinates are unknown, the method comprising:
 exchanging radio waves between the first and the second base stations;   measuring a distance between the first and the second base stations based on a result of exchanging radio waves between the first and the second base stations;   calculating position coordinates of the second base station based on the measured distance;   determining a time reference station out of the base stations;   controlling the time reference station to transmit a time reference pulse;   calculating a time difference between reception times at which the base stations receive the wave signal from the mobile terminal; and   calculating position coordinates of the mobile terminal based on the time difference.   
   
   
       13 . The method according to  claim 12 , wherein the determining includes calculating maximum values of distances between the respective base stations and the other base stations based on the result of the measurement to determine a base station having a smallest maximum value among the calculated maximum values as the time reference station. 
   
   
       14 . The method according to  claim 12 , further comprising:
 selecting a base station out of the plurality of base stations; and   counting a number of other base stations, distances to which from the selected base station can be measured, wherein   the determining includes determining the time reference station based on a result of the counting of the counting unit, a base station having a largest number of other base stations, distances to which from the selected base station can be measured.   
   
   
       15 . The method according to  claim 12 , wherein the determining includes
 measuring distances from the other base stations a plurality of times in the distance measuring unit for each of the base stations,   calculating fluctuations in the measured distances, calculating maximum values of the fluctuations, and   determining a base station having a smallest maximum value among the calculated maximum values as the time reference station.   
   
   
       16 . The method according to  claim 12 , further comprising monitoring a reception state in a base station that receives the time reference pulse, wherein
 the determining includes switching the time reference station, when determining based on a result of the monitoring of the reception-state monitoring unit that the base station does not receive the time reference pulse for a predetermined time or more.   
   
   
       17 . The method according to  claim 16 , wherein the determining includes determining, based on the result of the measurement and the result of the monitoring, priority order of the base station that transmits time reference pulse, and switching, based on the determined priority order, the base station that transmits the time reference pulse. 
   
   
       18 . The method according to  claim 17 , further comprising controlling the base stations to transmit the time reference pulse from different base stations at first timing and second timing, wherein
 the determining includes determining the time reference station, based on reception states in the respective base stations of the time reference pulse transmitted at the first timing and reception states in the respective base stations of the time reference pulse transmitted at the second timing.   
   
   
       19 . The method according to  claim 12 , wherein the measuring includes measuring distances among the respective base stations at every predetermined time. 
   
   
       20 . The method according to  claim 19  wherein the measuring includes measuring distances among the respective base stations at timing different from timing when the time reference pulse is transmitted. 
   
   
       21 . The method according to  claim 12 , wherein an ultra wide band (UWB) pulse is used for radio communication among the base stations and radio communication between the respective base stations and the mobile terminal.